1) Field of the Invention
The present invention relates generally to an electronic ballast that provides both dual power output for use with two different wattage lamps and dimming capability wherein either wattage lamp can be dimmed.
2) Problem to be Solved
Electronic ballasts that provide a bi-level output for use with different wattage lamps are known in the art. Some examples of these electronic ballast are described in U.S. Pat. Nos. 5,327,048 and 6,204,614. Ballasts that provide dimming capability are also known in the art. Examples of these types of ballasts are described in U.S. Pat. Nos. 5,327,048, 5,559,395 and 6,204,614. However, the ballast described in the aforementioned patents cannot simultaneously provide dual-power capability for powering either a relatively higher wattage lamp and a relatively lower wattage lamp and effect dimming of either lamp. What is needed is an electronic ballast that is configured to provide a bi-level (or dual power) output for powering two different wattage lamps and at the same time, enable dimming of either lamp.
In a first aspect, the present invention is directed to control circuitry for controlling the output power of an electronic ballast system having a power supply branch circuit having power lines comprising a line voltage line and a common line, and a ballast stage having (i) inputs connected to the power lines for providing power to a lamp, (ii) internal power control feedback circuitry that defines a feedback loop for controlling the amount of power applied to the lamp, and (iii) a control signal input for receiving a control signal that affects operation of the internal power control feedback circuitry and the level of power outputted by the ballast stage. In one embodiment, the control circuitry comprises a first circuit having an input for connection to one of the power lines. The first circuit generates a control signal for input into the control signal input of the ballast stage. The control circuitry has a first predetermined magnitude when one of the power lines is connected to the input of the first circuit and a second predetermined magnitude when neither of the power lines is connected to the input of the first circuit. The control circuitry further comprises a second circuit having a first state for reducing the first and second predetermined magnitudes of the control signal by a predetermined increment so as to effect step dimming of the high intensity discharge lamp and a second state that maintains the first and second predetermined magnitudes of the control signal so as to effect operation of the lamp at full brightness.
In one embodiment, the second circuit includes an input for receiving one of the power lines and is configured to be responsive to the application of one of the power lines to the input of the second circuit. The second circuit has the first state when one of the power lines is connected to the input of the second circuit and the second state when neither of the power lines is connected to the input of the second circuit.
In another embodiment, the second circuit includes an input for receiving one of the power lines and is configured to be responsive to the application of one of the power lines to the input of the second circuit. The second circuit has a first state when neither one of the power lines is connected to the input of the second circuit and the second state when one of the power lines is connected to the input of the second circuit.
A feature of the control circuitry of the present invention is that it can be used with different types of arc discharge lamps, such as HID lamps and fluorescent lamps.